Real-time estimation of the time-varying transmission advantage of Omicron in England using S-Gene Target Status as a Proxy

• Updated the summary text to reflect post-Christmas changes.
• Updated the time at 95% Omicron plot to include median estimates. This was needed to prevent estimates disappearing when uncertainty was less than or equal to a day.
• Fixed a bug for the centred 7-day moving average where partially complete case data was included for regions. This impacted on the data overview plot.

Full Changelog: https://github.com/epiforecasts/omicron-sgtf-forecast/compare/v1.2.0...v1.3.0